thesis - Faculty of Information and Communication Technologies ...

Chapter 5. Growth Dynamics
of wealth.
The results from our study showed that metric distributions have a
similar shape across a range of different systems. These distributions
are stable over long periods of time with occasional and abrupt spikes
indicating significant changes are rare. A general pattern is that once
developers commit to a specific solution approach, the organisational
preferences are stable as the software system evolves.
An unexpected finding of this study was the observation that systems
containing machine generated code have distributions that are significantly
more skewed. Based on this unique profile we developed a technique
that can be used to automatically detect the presence of generated
code — a technique that can greatly aid software comprehension as well
as to assist in software reviews.
Our analysis shows that the popularity of a class is not a function of
its size or complexity, and that evolution typically drives these popular
classes to gain additional users over time. This finding provides empirical
support for the Yule process, also known as the preferential attachment
growth model. Interestingly, measures of size and structural
complexity do not show generalizable pattern. That is, large and complex
classes do not get bigger and more complex over time purely due to
the process of evolution, rather there are other contributing factors that
determine which classes gain complexity and volume. Identification of
these factors is an area that we leave as future work.
Given that popular classes in general gain additional popularity in evolving
software, a natural question that arises is – “does this growth in
popularity place any pressure on popular classes to change?” Lehman’
Laws of Software Evolution [174] suggest that software systems, due to
their very use, provide evolutionary pressures that drive change. Would
classes due to their popularity also undergo modifications? Although,
this was not an initial research question that we set out to answer in our
study, we added it into our study of the nature of change and discuss
our findings in the next chapter.
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